Immediate and overnight recumbence-dependent changes of neck circumference: relationship with OSA severity in obese...

Overnight increases in neck circumference - attributed to rostral fluid displacement - correlate with the severity of obstructive sleep apnea (OSA). No studies were found investigating the relationship between OSA severity and recumbence-related immediate changes in neck circumference. We evaluated the relationship of OSA severity with immediate recumbence-related and overnight changes in neck circumference in obese and nonobese subjects.

Male patients undergoing full-night in-laboratory polysomnography had their neck and ankle circumferences determined before and after sleep, both while standing and supine. Circumference changes were calculated by the difference between standing and recumbent positions (Immediate Change) and between before and after sleep (Overnight Change).

Immediate Change in neck circumference showed a linear significant correlation with apnea-hypopnea index (AHI; r=0.37373; p=0.012) and with lowest O2 saturation (r=-0.35355; p=0.017). In a multivariate model to predict AHI, adjusting for age and obesity, Immediate Change in neck circumference is the only significant regressor (beta=0.34; p=0.03). The Overnight Change in neck circumference correlated neither with the AHI nor with the lowest SaO2.

Correlation of AHI with the immediate increase in neck circumference on assuming recumbence indicates that fast components of tissue displacement, besides overnight fluid displacement, may have implications in the pathogenesis of OSA.